In transmitting data over multipath channels, the transmitted data symbols create interference at the receiver. The interference can be eliminated in the receiver if the pulse response of the channel is known, such as can be inferred from K. D. Kammeyer, “Communication Transmission,” Second Edition, Information Technology Series, Teubner, Stuttgart, 1996, and from A. Klein, G. K. Kaleh, and P. W. Baier, “Zero Forcing and Minimum Mean-Square-Error Equalization for Multiuser Detection in Code Division Multiple Access Channels,” IEEE Transportation Vehicle Technology, Volume 45 (1996), 276-287. The channel pulse response can be computed, e.g., in the receiver from a received reference signal.
However, interference can also be eliminated in the transmitter if the channel pulse responses are known there. Then the channel pulse response no longer needs to be computed in the receiver. In other words, transmission of a reference signal is then not necessary.
It is also possible to combine transmission systems that have interference elimination in the receiver and systems that have elimination in the transmitter, as is known from Bosch, “Mixed Use of Joint Predistortion and Joint Detection in the UTRA TDD mode,” ETSI Tdoc SMG2 UMTS-L1 205/98.
Because in data transmission systems that support interference elimination both in the receiver and in the transmitter the transmitted reference signal is superfluous when elimination is performed by the transmitter, the transmitted reference signal then occupies transmission capacity unnecessarily. If, when elimination is performed by the transmitter, an individualized transmission format is used, then the corresponding transmission devices are more complex (e.g., as a result of the channel coding designs that become necessary) and/or the data services of the two transmission modes are different.